Waveguide mode transducer

ABSTRACT

A transducer for converting the TE20 rectangular wave mode into the TM11 circular wave mode utilizes a circular waveguide capable of supporting the TM11 mode which is mounted to a broad side of a rectangular waveguide transmitting the TE20 wave mode. Two antiphase coupling ports formed at prescribed distances from the center of the circular waveguide and along a diameter thereof which is perpendicular to the longitudinal axis of the rectangular waveguide transfer energy from the TE20 wave mode into a substantially pure TM11 mode in the circular guide when the proper electrical and magnetic field patterns are obtained at the ports by adjusting a movable plunger within the rectangular waveguide.

United States Patent Den [54] WAVEGUIDE MODE TRANSDUCER [72] Inventor: Chi Fu Den, Summit, NJ.

[73] Assignee: Bell Telephone Laboratories, Incorporated,

Murray Hill, NJ.

[22] Filed: Mar. 12, 1971 [21] AppLNo; 123,673

[52] US. CL ..333/21 R, 333/98 R [51] Int. Cl. ..1l01p 1/16 [58] FieldofSearch ..333/2l,2l A, 98R

[56] References Cited UNITED STATES PATENTS 2,619,539 11/1952 Fano ..333/2l 2,851,681 9/1958 Cohn.....

2,939,094 5/1960 Berk ..333/2l 3,001,193 9/1961 Marie ..333/21X [4 1 Feb. 29, 1972 Primary Examiner-Eli Lieben'nan Assistant ExaminerMarvin Nussbaum Attorney-R. J. Guenther and Edwin B. Cave [5 7] ABSTRACT A transducer for converting the TH, rectangular wave mode into the TM circular wave mode utilizes a circular waveguide capable of supporting the TM mode which is mounted to a broad side of a rectangular waveguide transmitting the Ta wave mode. Two antiphase coupling ports formed at prescribed distances from the center of the circular waveguide and along a diameter thereof which is perpendicular to the longitudinal axis of the rectangular waveguide transfer energy from the TE wave mode into a substantially pure TM. mode in the circular guide when the proper electrical and magnetic field patterns are obtained at the ports by adjusting a movable plunger within the rectangular waveguide.

10 Claims, 7 Drawing Figures PATENTEDFEB 2 9 I972 SHEET 1 [IF 3 PAIENIEBFEB 29 I972 SHEET 2 [IF 3 HIUIHu HI II III WAVEGUIDE MODE TRANSDUCER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to wave mode transducers and more particularly to a transducer for generating the TM circular wave mode from the TE rectangular wave mode.

2. Description of the Prior Art A major source of signal attenuation and distortion in a waveguide transmission system is the conversion and reconversion between the desired mode of propagation and spurious wave modes. In a TE waveguide transmission system one of the most troublesome of these spurious modes is the TM circular wave mode because of the substantial similarity in phase constants of this mode and the TE mode. Thus, it is often desirable to test new waveguide apparatus such as mode filters to determine their effectiveness in removing undesirable spurious modes such as the TM mode. Because the output of most millimeter wave generators is a rectangular wave mode such as the TE mode it consequently becomes necessary to transform such rectangular wave modes into the required TM circular wave mode.

Various transducer designs have been proposed for generating the TM, wave mode from available rectangular wave modes. However, it is believed that none of these previous designs provides a sufficiently pure TM mode for testing applications. Further, the bandwidth of these known transducers is not sufficiently broad to permit testing of apparatus across the broad frequency ranges which will be utilized in a waveguide transmission system.

Accordingly, it is an object of this invention to improve the apparatus for generating the TM circular wave mode.

Another object is to improve TM circular wave mode transducers so that the TM mode can be generated over a broad frequency range.

A more specific object is to improve the apparatus for obtaining the TM circular wave mode from readily available.

rectangular wave modes. I

SUMMARY OF THE INVENTION The foregoing objects and others are achieved in accordance with the principles of the invention by a transducer. comprising a circular waveguide section capable of supporting 45 section containing the TE rectangular wave mode from? the TM circular wave mode and a rectangular waveguide which the TM wave mode is to be derived. The rectangular waveguide section may include a transducing section for con-.

verting some other readily available rectangular wave mode, such as the TB mode, into the TE mode. The circular L waveguide is mounted perpendicular to a broad face or side of the rectangular waveguide section and is electrically terwaveguide section.

DESCRIPTION OF THE DRAWING The invention will he more fully comprehended from the following detailed description and accompanying drawing in which:

FIG. I is a schematic representation of a segment of a circular waveguide showing the electric field distribution for the TM wave mode therein;

FIG. 2 is an embodiment of the transducer according to the W ii1\/ en ti on for generating the TM circular wave modgfrom the TF rectangular wave mode; n I v FIG. 3 is a schematic representation of the electric field configuration of the TF wave mode in the rectangular guide section of FIG. 2;

FIG. 4 is an embodiment of a transducer for obtaining the TE rectangular wave mode from the TE rectangular wave mode;

FIG. 5 is a schematic representation of a sectional view along the line =0 of FIG. 2 of another embodiment of a TIE,

I to TM transducer utilizing dielectric sphere coupling; FIG. 6 is a schematic representation of a sectional view along the line =0 of FIG. 2 of still another embodiment of a TE to TM transducer utilizing dipole coupling; and

FIG. 7 is a perspective schematic representation partly in section of yet another embodiment of a T5,, to TM trans ducer utilizing loop coupling.

DETAILED DESCRIPTION Referring now to FIG. 1, in the plane z=0 of circular waveguide section 101 there are two points 2 and 4 where the electric field of the TM wave mode is relatively concentrated. These points 2 and 4 lie along a diameter 6 of section 101 and in the directions defined by the angle =0 and 11', respectively. By a solution of the equations for the electric and magnetic field components in the plane of z=0, the distances 8 and 10 of points 2 and 4, respectively, from the center 12 of waveguide section 101 are found to be 0.4805 of a radius 14.

At points 2 and 4 the z-component Ez of the electric field becomes maximum and minimum, respectively, while the two electric field components E, and E and the magnetic field components HrvlH all equal zero Thus, the TM, circular wave mode couldFe excited in section 101 by requiring the field patterns in the plane z=0 to be as follows: Ez=K in an incremental radius circle centered at point 2, and K in-an incremental radius circle centered at point 4 where K a constant; and BQ II-LQL all equal zero. All other TM, circular wave modes such as the TM and the TM, modes having cutoff frequencies less than or only slightly larger than the eutoff frequency of the TM mode will not be excited by the specified field patterns.

From the foregoing it is apparent that the generation of the TM, circular wave mode can be obtained by the introduction of z-directed electric fields equal in magnitude but opposite in I phase through matched coupling ports located at points 2 and 4. Turning now to FIG. 2 there is shown a transducer design for obtaining such introduction of properly directed electric fields. FIG. 2 shows circular waveguide section 101 mounted perpendicular to a rectangular waveguide section 102 so that circular section 101 is electrically terminated in a broadside or face 16 of rectangular waveguide section 102. Two matched holes or apertures 18 and 20-are located in face 16. Holes 18 and 20 are positioned symmetric with centerline 22 of face 16 and midway between centerline 22 and outer edges 26 and 28, respectively. That is, the distance 24 of holes 18 and 20from centerline 22 equals one-fourth of the width 30 of face 16. The centers of holes 18 and 20 coincide with points 2 and 4, respectively, which, as previously discussed, lie along a diameter 6 of circular waveguide 101 at a distance of 0.4805 of radius 14 from the center 12 of the section 101. Thus, it readily can be shown that diameter 6 equals 1.041 times the width 30 of face 16.

Rectangular waveguide 102 transmits the TE, wave mode as indicated which was derived from a millimeter wave generator as will be subsequently described. As shown in FIG. 3 the electric field pattern of the TB rectangular wave mode' has peak amplitudes at distances 23, which equals distance 24, from a vertical plane 32 through centerline 22 and decreases to zero at plane 32 and at each of the narrow sides of waveguide 102. The peak amplitudes on either side of plane ,32 are equal in magnitude but opposite in phase. These peak amplitudes are aligned with coupling holes 18 and 20. Hence, the field patterns previously specified for the generation of the TM wave mode in circular waveguide section Ltl I wig e xist when the electric field in section 102 is properly located in the z-direction. The proper z-direction loczfiion is obtaified by tlie adjustment of the position of a plunger 34 which is slideably mounted in one terminal or end of rectangular waveguide sec- \tion 102. Plunger 34 is made of a conducting material. By adjusting the position of plunger 34 electric and magnetic field patterns corresponding to the pattern shown for the plane z= in FIG. 1 can be obtained at a plane along axis =0 through holes 18 and 20 which is transverse to side 16. When the electric field of the TF mode is properly positioned in waveguide 102, the electric fields appearing in holes 18 and 20, which are equal in magnitude but opposite in phase, become maximum. The electric fields in matched holes 18 and 20 can be considered as the equivalent of matched electric dipoles polarized in the direction of the electric field in the respective holes. Consequently, matched holes 18 and 20 act as matched coupling ports which excite a substantially pure TM wave mode in circular waveguide 101.

Designs other than the relatively simple design using matched holes 18 and 20 can also be utilized as coupling ports. One such design involves filling matched holes 18 and 20 with matched dielectric spheres 36 and 38, respectively, as schematically shown in H6. 5. Dielectric sphere coupling ports are particularly advantageous when the thickness 37 of the broad face 16 is equal to or greater than one-fourth of the diameters of the coupling holes 18 and 20. At such thicknesses the hole itself acts like a small waveguide which may be below cutoff for the desired coupling wave. Dielectric spheres 36 and 38 in essence make electrically small holes appear larger and thus keep these holes above cutoff for the coupling waves.

Another alternative coupling port design utilizes matched conducting rods or probes 44 and 46 which are mounted in insulators 48 and 50, respectively, in holes 18 and 20 as shown in FIG. 6. The current on probes 44 and 46 caused by the electric field of the TE wave mode in waveguide 102 will be equal in magnitude but opposite in phase. Thus, the probes will excite a substantially pure TM mode in circular waveguide 101. This particular coupling port design is advantageous in relatively low-frequency ranges. Since the probes act as coaxial conductors the losses at higher frequencies tend to become unacceptably high.

in all of the previously discussed coupling port designs, coupling to the electric field of the TE, rectangular wave mode has been utilized. Thus, the position of plunger 34 is adjusted to obtain a maximum electric field in the plane of the coupling ports. Still another embodiment of a coupling port design utilizing matched conducting rods 52 and 54 with looped ends which couple to the magnetic field of the T wave mode is illustrated in FIG. 7. Rods 52 and 54 are mounted in insulators 53 and 55, respectively, in holes 18 and 20. The portions of rods 52 and 54 in rectangular waveguide 102 are in the form of loops which lie in planes parallel to the narrow sides 57 and 59 of waveguide 102 and the tips 49 and 51 of the loops are soldered to broad face 16. The other ends of S2 and 54 extend into circular waveguide 101 as monopole elements. The looped ends of rods 52 and 54 readily couple to .the magnetic field of the TE wave mode; hence, in this coupling design plunger 34 is adjusted to obtain a maximum magnetic field rather than a maximum electric field in the plane of the coupling ports. This coupling port design is advantageous in low-frequency ranges. At higher frequencies the coaxial type losses become troublesome.

Many presently available millimeter wave generators produce the TE rectangular wave mode. Thus, a conversion of transformation of this TE mode is required to obtain the TE mode which is needed in rectangular waveguide section 102 of this invention. FIG. 4 shows a transducer 103, which is known in the prior art, for making the required transformation. The TE, output from a wave generator which is not shown is transmitted to a rectangular input waveguide section 62 having a width 58 equal to one-half the width of face 16 of waveguide section 102. A ramped section 64 merges into section 62. The wall between sections glangiqjsrgmovedform;

ing an aperture 65 which extends the entire length 60 of ramped section 64. Ramped section 66 terminates in a rectansection 68. Thus, the output of transducer 103 can be mated with the input end 17 of waveguide section 102 to obtain a complete TE to TM wave mode transducer. Various other types of transducers might also be used to generate the TE rectangular wave mode from initial modes produced by wave generators.

While the invention has been described with reference to a specific embodiment thereof, it is to be understood that various modifications thereto might be made by those skilled in the art without departing from the spirit and scope of the foregoing description and the following claims.

What is claimed is:

1. A waveguide mode transducer comprising, in combination:

a rectangular waveguide for propagating an electromagnetic wave in a first mode, said rectangular waveguide having two apertures formed in one of the broadsides thereof, said two apertures being symmetric with the lonwaveguide so that preselected fields can be obtained at 3 said apertures whereby said second mode is excited in said circular waveguide. 2. Apparatus in accordance with claim 1 wherein said first mode comprises the TB, rectangular wave mode, said plunger is adjusted to obtain an electric field maximum and a magnetic field minimum at said apertures so that the electric fields in said apertures are equal in magnitude and opposite in phase whereby the TM circular wave mode is excited in said circular waveguide.

3. Apparatus in accordance with claim 2 including spheres of dielectric material mounted in said apertures for maintaining said apertures above cutoff when the thickness of said one broadside is equal to or greater than one-fourth of the diameters of said apertures.

4. Apparatus in accordance with claim 2 including an insulator mounted in each of said apertures and a conducting rod inserted through each of said insulators so that said rods constitute dipoles extending from said rectangular waveguide into said circular waveguide.

5. Apparatus in accordance with claim 1 including insulators mounted in each of said apertures and a conducting rod inserted through each of said insulators and having the first 1 and second ends therein extending into said rectangular waveguide and said circular waveguide, respectively, said first i end being formed into a loop lying in a plane parallel to the narrow sides of said rectangular waveguide with the tip of said first end electrically connected to said one broadside, said first mode comprising the TE; rectangular wave mode, said plunger is adjusted to obtain a magnetic field maximum and an electric field minimum at said apertures so that the TM circular wave mode is excited in said circular waveguide.

6. Apparatus in accordance with claim 1 wherein said apertures are located equidistant between said centerline and the d e-"2P? se ans Puss es @5 9 i l. isuse: dismisses;

waveguide is greater than the width of said one broadside. 7 10. A modetransducer for transforming the TE rectan ui 7. Apparatus in accordance with claim 6 wherein said El mellfifilfiie Circular Wv made 'r fi g; diameter of said circular waveguide equals 1.041 times said in Combination! width of said broadside. an initial transducer for transforming said TE mode to the 8 Apparatus in accordance with claim 1 wherein said 5 TE rectangular wave mode; and plunger comprises a conductive material. a final transducer connected to the output of said initial 9. A waveguide mode transducer for transforming the TE transducer for transforming said TE mode to said TM rectangular wave mode to the TM circular wave mode commode, said final transducer including: prising, in combination: a rectangular waveguide for receiving said TE, mode;

a rectangular waveguide Containing Said zo mode; a circular waveguide capable of supporting said TM circua circular Waveguide Capable of pp g Said mode lar mode, said circular waveguide being mounted normal Said Circular Waveguide being mounted normal to a to a broadside of said rectangular waveguide and symmetbroadside of said rectangular waveguide and symmetric tic with the longitudinal t li th f;

with the longitudinal center line thereof; first and second coupling ports formed in said broadside for 15 coupling electromagnetic energy between said rectangular waveguide and said circular waveguide, said ports being symmetrically positioned with respect to said centerline and along a diameter of said circular waveguide which is perpendicular to said centerline; and a plunger slideably mounted within said rectangular waveguide for adjusting the position of the electric and magnetic fields of said TE mode so that preselected fields can be obtained at said ports whereby said TM fields can be obtained at sald ports whereby said mode is excited in said circular wave uide. mode is excited n sa isecond wavegu de. V M 7 if "77 t a g terline and along a diameter of said circular waveguide which is perpendicular to said centerline; and

a plunger slideably mounted within said rectangular waveguide for adjusting the position of the electric and magnetic fields of said TE mode so that preselected first and second coupling ports in said broadside for; coupling electromagnetic energy between said rectangular waveguide and said circular waveguide, said ports being symmetrically positioned with respect to said cen- 

1. A waveguide mode transducer comprising, in combination: a rectangular waveguide for propagating an electromagnetic wave in a first mode, said rectangular waveguide having two apertures formed in one of the broadsides thereof, said two apertures being symmetric with the longitudinal centerline of said one broadside; a circular waveguide mounted normal to said one broadside and electrically terminated therein, said circular waveguide being symmetric with respect to said centerline so that said two apertures are located along a diameter of said circular waveguide which is perpendicular to said centerline, said circular waveguide being capable of supporting an electromagnetic wave of a second mode; and a plunger slideably mounted in one end of said rectangular waveguide for adjusting the location of the electric and magnetic fields of said first mode within said rectangular waveguide so that preselected fields can be obtained at said apertures whereby said second mode is excited in said circular waveguide.
 2. Apparatus in accordance with claim 1 wherein said first mode comprises the TE20 rectangular wave mode, said plunger is adjusted to obtain an electric field maximum and a magnetic field minimum at said apertures so that the electric fields in said apertures are equal in magnitude and opposite in phase whereby the TM11 circular wave mode is excited in said circular waveguide.
 3. Apparatus in accordance with claim 2 including spheres of dielectric material mounted in said apertures for maintaining said apertures above cutoff when the thickness of said one broadside is equal to or greater than one-fourth of the diameters of said apertures.
 4. Apparatus in accordance with claim 2 including an insulator mounted in each of said apertures and a conducting rod inserted through each of said insulators so that said rods constitute dipoles extending from said rectangular waveguide into said circular waveguide.
 5. Apparatus in accordance with claim 1 including insulators mounted in each of said apertures and a conducting rod inserted through each of said insulators and having the first and second ends therein extending into said rectangular waveguide and said circular waveguide, respectively, said first end being formed into a loop lying in a plane parallel to the narrow sides of said rectangular waveguide with the tip of said first end electrically connected to said one broadside, said first mode comprising the TE20 rectangular wave mode, said plunger is adjusted to obtain a magnetic field maximum and an electric field minimum at said apertures so that the TM11 circular wave mode is excited in said circular waveguide.
 6. Apparatus in accordance with claim 1 wherein said apertures are located equidistant between said centerline and the edges of said one broadside, and said diameter of said circular waveguide is greater than the width of said one broadside.
 7. Apparatus in accordance with claim 6 wherein said diameter of said circular waveguide equals 1.041 times said width of said broadside.
 8. Apparatus in accordance with claim 1 wherein said plunger comprises a conductive material.
 9. A waveguide mode transducer for transforming the TE20 rectangular wave mode to the TM11 circular wave mode comprising, in combination: a rectangular waveguide containing said TE20 mode; a circular waveguide capable of supporting said TM11 mode, said circular waveguide being mounted normal to a broadside of said rectangular waveguide and symmetric with the longitudinal center line thereof; first and second coupling ports formed in said broadside for coupling electromagnetic energy between said rectangular waveguide and said circular waveguide, said ports being symmetrically positioned with respect to said centerline and along a diameter of said circular waveguide which is perpendicular to said centerline; and a plunger slideably mounted within said rectangular waveguide for adjusting the position of the electric and magnetic fields of said TE20 mode so that preselected fields can be obtained at said ports whereby said TM11 mode is excited in said second waveguide.
 10. A mode transducer for transforming the TE10 rectangular wave mode into the TM11 circular wave mode comprising, in combination: an initial transducer for transforming said TE10 mode to the TE20 rectangular wave mode; and a final transducer connected to the output of said initial transducer for tRansforming said TE20 mode to said TM11 mode, said final transducer including: a rectangular waveguide for receiving said TE20 mode; a circular waveguide capable of supporting said TM11 circular mode, said circular waveguide being mounted normal to a broadside of said rectangular waveguide and symmetric with the longitudinal centerline thereof; first and second coupling ports in said broadside for coupling electromagnetic energy between said rectangular waveguide and said circular waveguide, said ports being symmetrically positioned with respect to said centerline and along a diameter of said circular waveguide which is perpendicular to said centerline; and a plunger slideably mounted within said rectangular waveguide for adjusting the position of the electric and magnetic fields of said TE20 mode so that preselected fields can be obtained at said ports whereby said TM11 mode is excited in said circular waveguide. 